The type I human T cell leukemia virus (HTLV-I) has been shown to cause an aggressive and often fatal neoplasm of mature T lymphocytes termed the adult T cell leukemia (ATL). This pathogenic retrovirus encodes a 40 kD polypeptide, tax, which acts in trans to greatly amplify transcription directed by the retroviral long terminal repeat. In addition to these effects, tax also has been found to deregulate the expression of two cellular genes, interleukin-2 (IL-2) and the alpha subunit of the IL-2 receptor, which play an important role in the regulation of normal T cell growth. These findings have raised the possibility that the interplay of tax with certain T cell genes may contribute to the leukemic transformation induced by HTLV-I. To delineate the full spectrum of cellular genes regulated by tax, subtracted cDNA probes will be prepared using isogenically matched Jurkat T cells stably expressing either sense or anti-sense tax cDNAs. These subtracted probes will be used to identify tax inducible mRNAs within a cDNA library prepared from HTLV-I infected HUT102B2 cells. These cDNAs will then be sequenced and characterized to identify their corresponding protein products. Additionally, these various genes will be analyzed for cell- or tissue-specific patterns of expression. To further investigate whether tax alone is sufficient for the transformation of human T cells, tax cDNAs will be stably introduced into primary T lymphocytes using a recently developed electroporation transfection technique. Analysis of potential alterations in gene expression and/or growth in these tax producing primary human T cells may provide important new insights into the effects of this viral protein on the regulation of T cell growth and activation. Together, these studies should lead to a clearer understanding of the mechanism of tax action and its role in HTLV-I induced leukemogenesis.